Okay, cruising in my 7, when I shift when the turbo spools, I hear a sound, kind of like when you open a pop bottle under pressure. I know it's the blowoff valve also, but I'm curious as to how it works, and why everyone I talk to thinks it's better to get a larger blowoff valve? What's the attraction, is it just better and more audible sounds when the pressure is released, or does it stabalise the air flow through the plumbing? Would I just be wasting my money if I was thinking to get another one?

 

um bacially its a spring loaded diaphram that sees vacuum/boost, under boost it gets blown shut (so its not a leak) and under vacuum it can open to vent pressure. if you have the stock turbo theres really no need for a larger valve than stock, unless you want the look/sound



mike

 

The BOV is designed to vent boost pressure to the atmosphere ( or back into the pre-turbo intake stream depending on application being used) when the throttle plates close. For example if you are @ 14 psi of boost and are changing gears, your turbo was just throwing 14 psi of air pressure @ xxx CFM that air will run into the closed throttle plates and bounce. The wave usually bounces all the way back to the compressor housing of the turbo. This has a tendancy to do two things. 1) it forces air into the compressor wheel, slowing it down and 2) a thing called compressore surge. Which basically throws a lot of turbulance against the compressor wheel which over a period of time will wear on the front bearing and thrust collar which will in turn necessitate a rebuild/replacement a lot sooner.



As far as upgrading you have to look at the amount of air you are trying to move and what type of pressures you are using. If you are upgrading to a larger turbo and FMIC than yes it is time to upgrade the BOV to a unit that can handle the amount of air flow required to vent enough gasses for that. When you get into the big single turbo combinations sound is no longer an option. The idea is to get the air our as fast as possible. A lot of guys running a large single (TO4E and larger) like to run the Greddy Type R BOV, this is one of the largest flowing BOV's on the market and has a 2 in+ opening to exhaust the air, in comparison, a loud greddy Super sound uses a small opening and does not vent nearly the same through its 1/2 vent square. If the guy can't tell you have a turbo by the time you are switching between first and second gear, there is no real need to tell him with some bird chirping under your hood each time you shift. If you still want the sound but want to go with a large BOV get that electronic BOV speaker system they have out for a N/A riceboy.

 

oh, I HATE that bird chirp sound. There is nothing worse, I'd rather hear a 2 stoke-engine at 10,000 rpm all night long than one of those stupid chirps.

 

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